Functional brain laterality in adulthood ADHD
|PhD ceremony:||dr. S.M.H. (Saleh) Mohamed, PhD|
|When:||March 06, 2017|
|Supervisor:||prof. dr. J.J. van der Meere|
|Co-supervisors:||dr. N.A. (Norbert) Borger, dr. R.H. Geuze|
|Where:||Academy building RUG|
|Faculty:||Behavioural and Social Sciences|
The present thesis aimed to address functional brain laterality and symptoms of Attention-Deficit/Hyperactivity Disorder (ADHD) in adults, from a dimensional perspective. The dimensional perspective assumes that ADHD symptoms are normally distributed in general population and those scoring at the high end of the distribution are at risk of being diagnosed with ADHD. Participants completed questionnaires designed to detect ADHD symptoms in adults. The scores were used to test how severity of ADHD symptomatology is associated with valid behavioral indices of functional brain laterality, interhemispheric interaction speed (using the divided visual field paradigm), state regulation, and error-processing. It appeared that all these behavioral indices as well as scores on the self-reported ADHD scales were, more or less, normally distributed.
Study 1 and 2 showed no (dimensional) associations between ADHD symptoms and interhemispheric interaction speed, right and left hemisphere-functioning. However, there is evidence that attentional processes in adults with the highest scores on inattention scale are related with less optimal right hemisphere-functioning than that in adults with the lowest inattention scores. Study 3 and 4 indicated that the higher ADHD scores are, the more defective regulation of motor activation (due to less effort allocation). This is particularly true when stimuli are presented to the right visual field at slower rate. Under such conditions, less optimal error-monitoring was observed. These findings underscore the association between left hemisphere-functioning and both effort allocation and error-processing in ADHD symptomatology. In sum, findings underline the role of atypical brain laterality in heterogeneous ADHD symptoms in adults.